Today, SunRun enters Pennsylvania, its sixth state. You wouldn’t think of Pennsylvania as a solar-friendly state but, as it happens, the Keystone State has all the right ingredients–high and rising electricity prices, generous state subsidies for renewable energy, and a regulatory framework that permits homeowners to sell surplus power back to the electricity grid.

Says Lynn Jurich, the president and co-founder of SunRun: “We want to go to markets where we can save customers money, and where we can make money.”

I’ve written about SunRun before (See SunRun: A New Deal for Solar and Solar’s Strange Bedfellows) but the company is growing so fast, albeit off a small base, that it makes a lot of news. The PG&E, Home Depot and Toll Brothers agreements, along with its geographic expansion, all seem to further validate the company’s business model.

As Jurich put it:

The top utility, the top home improvement company, and one of the top 5 builders in the country are all working with SunRun…Residential solar is finally going mainstream.

Well, not quite yet–SunRun has about 5,000 customers, just a few more than the little village where I grew up. Solar panels, while coming down in cost, remain a much more expensive way than coal or natural gas to generate electricity, so they are dependent upon a variety of government subsidies. Some homeowners don’t like the way panels on the roof look.

But SunRun has removed two big obstacles to the mainstreaming of solar–the upfront costs and the hassle factor. Purchasing a solar system outright can cost $25,000 to $45,000, but because SunRun owns and maintains its systems, homeowners frequently don’t have to pay any money down. The company works with reputable local installers, and makes technology decisions that could confound newbies to the field.

“If you can remove all the hassles, we think solar can be a very mainstream product,” Jurich says. “Our biggest barrier, really, still, is education. People don’t know that they have an alternative to the utility company. You can get some of your power from your rooftop and we will manage the whole thing for you.”

In essence, SunRun is a service, financing and marketing operation–it doesn’t actually make anything. The company raises the money to buy the systems, arranges the installations, takes advantage of a 30% federal tax credit that’s available to home owners who install solar energy, monetizes the Renewable Energy Credits or RECs available in many states, and collects monthly electricity payments from homeowners. If the business model works, those revenue streams, taken together, are sufficient to repay its lenders (like PG&E), pay its own costs and generate a profit.

Jurich told me that SunRun has, so far, raised enough money to pay for about $300 million worth of solar installations. She expects that figure to climb past $1 billion in the next year or two. That’s impressive for a company that got its start less than four years ago when Jurich and Ed Fenster, SunRun’s CEO, were MBA students at Stanford.

Of course, SunRun isn’t the only solar home financing company. It’s got competition from, among others, Solar City, which is backed by celebrity entrepreneur Elon Musk. BYD, the Chinese electric car and battery company, last spring struck a deal with KB Home, to install solar panels in a new development of modestly priced homes in Lancaster, CA. (See Warren Buffett’s BYD: Revving up Fast) I’m sure there are other solar financing firms out there that haven’t gotten my attention.

But the competition should be good for everyone involved, not least the customers.

As Jurich told me: “If residential solar works—residential electricity is a $150 billion market—there’s plenty of business to go around.”

Marc Gunther is a writer and speaker who focuses on business and the environment. He worked for 12 years as a senior writer at FORTUNE magazine, where he is now a contributing editor. His most recent book, "Faith and Fortune: How Compassionate Capitalism is Transforming American Business," was published by Crown in 2004.

A guest says:

We are in our third year of having solar panels on our roof and it was a very good decision for our family. Our first end of year "true up" time we paid $16.oo for our annual electric use. The second year it was about $400 for the entire year. We are a household that uses a lot of electrical computers, gaming equipment etc and our power usage was high before. Now we watch our usage for things like laundry and do them in off peak hours. The solar panels use "free" energy from the sun that is not harmful and will not cause any radiation or pollution.